This invention relates to an electronic camera, particularly to an electronic camera which can correct an obliquely viewed object image into a photographic image viewed from front.
Electronic cameras have, as compared with conventional cameras which record images on a silver-salt film, an advantage of picking up images of satisfactory quality by suitably applying an image quality processing to the picked up images according to photographing purposes and types of objects since the quality of the photographed image can freely be processed. Thus, the electronic cameras are used as apparatus not only for usual picture taking, but also for photographing an information such as characters and graphics drawn on a white board at, e.g., a conference hall.
At the conference hall, the seats of participants are normally arranged with respect to the white board. Accordingly, if figures, characters or the like drawn on the white board are photographed without moving the seats, the photographed images are oblique images. Since the entire information such as characters drawn on the white board cannot be focused when photographing is performed obliquely with respect to the white board, a perspective geometric distortion is found in the photographed image, making it difficult to read such photographed information.
In order to avoid the problem of oblique images, the photographing position may be moved to a front position with respect to the white board. However, since it is difficult to move the photographing position during the conference, it is remarkably advantageous that the camera be provided with a function of photographing an image while correcting the geometric distortion thereof (i.e., a function of photographing while correcting an oblique image into a pseudo front image).
A variety of techniques for correcting the geometric distortion of a photographed image resulting from oblique photographing have been proposed.
For example, Japanese Unexamined Patent Publication No. 57(SHO)-129080 discloses a method for detecting or designating a specified position of an image, obtaining a normalized coefficient of this position with respect to a position on a sensing surface which this position is supposed to be located, and correcting an image distortion by applying a coordinate transformation to the input image in accordance with the obtained coefficient.
Further, Japanese Unexamined Patent Publication No. 3(HEI)-94383 discloses a method for supposing a known fixed geometry, arranging an input image within this fixed geometry, obtaining a transformation coefficient based on a deformed state of this fixed geometry, and correcting an obliquely photographed image by applying a transformation to the input image in accordance with the obtained coefficient.
Furthermore, Japanese Unexamined Patent Publication No. 5(HEI)-101221 discloses a method for superimposing an orthogonal lattice on an object surface, obtaining space coordinates of orthogonal lattice points, projecting a light while applying an orthogonal transformation to coordinate systems defined on a sensing surface, and correcting an obliquely photographed image by performing an offset calculation such that the luminance at a projection point is the luminance at the corresponding lattice points on the sensing surface.
However, according to the methods disclosed in the above publications, when the obliquely photographed image is to be corrected, a specified information needs to be input. Thus, it is difficult to perform photographing while the obliquely photographed image is corrected into a pseudo front photographed image by a simple operation.
More specifically, according to the method of the first publication, for the correction of the obliquely photographed image, a plurality of positions of the input image need to be designated to calculate a coordinate transformation coefficient. According to the method of the second publication, an image to be photographed needs to be arranged within an image of known fixed geometry. According to the method of the third publication, the two dimensional coordinates of the lattice points need to be input by superimposing the orthogonal lattice on the object surface and projecting the respective lattice points. It is extremely difficult to perform the above operations during picture taking.
Further, according to the above methods, since the obliquely photographed image is corrected into a pseudo front photographed image by coordinate transformation, the correction is complicated and it is difficult to rapidly perform it .
On the other hand, in an oblique photographic scene, the sensing surface and the object surface are normally parallel to each other along the vertical direction, but inclined to each other in a horizontal plane. Accordingly, assuming that xcex8, S and m denote an angle of inclination, an object image and a photographing magnification, an oblique image projected on the sensing surface of the camera is mxc2x7S cos(xcex8). Thus, if the angle of inclination xcex8 and the photographing magnification m are known, the oblique image can be corrected into a front image based thereon by a simple operation.
In view of the above, an electronic camera has been proposed which can calculate a distribution of photographing magnification m within the obliquely photographed image based on the angle of inclination xcex8 and a distance to the object and correcting the obliquely photographed image into a front image using the angle of inclination xcex8 and the distribution of photographing magnification m .
A variety of methods may be adopted to correct the distortion of an obliquely photographed image based on the angle of inclination xcex8 and the distribution of photographic magnification m. For example, the obliquely photographed image may be corrected into a pseudo front image by applying image compression to a portion of the obliquely photographed image closer than a focus position (normally, center position of the photographed image), while applying image enlargement to a portion thereof more distant that the focus position. Further, the obliquely photographed image may be corrected into a pseudo front image by using one end of the obliquely photographed image as a reference and applying image enlargement to the entire image at the other end. In such cases, the enlarged image may bulge out of the field, and a portion of the obliquely photographed image may be missing due to the correction. If a missing portion becomes larger, a necessary image cannot be photographed, with the result that the function of correcting the distortion of the obliquely photographed image may end up causing problems.
It is extremely difficult for a camera operator to predict the missing portion after correction based on the angle of inclination and an object obliquely viewed through a viewfinder. Normally, the presence or absence of the missing portion of the image and the range thereof cannot be confirmed unless the photographed image is printed out. Accordingly, an ability to confirm a range where the distortion of the obliquely photographed image is correctable before photographing is desirable for the above mentioned image distortion correcting method.
Further, according the above image distortion correcting method, unless the angle of inclination xcex8 is accurately input, the distortion of the obliquely photographed image is improperly corrected, resulting in an unnatural photographed image. Accordingly, an angle of inclination setting member of the camera needs to relatively accurately set the angle of inclination xcex8. On the other hand, if the camera requires a complicated operation to set the angle of inclination, the operability for photographing is reduced and the image distortion correcting function cannot effectively be utilized. Therefore, the setting member should be able to easily and rapidly set the angle of inclination xcex8.
For example, in the case that the camera operator sets the angle of inclination between the sensing surface and the object surface, there can be considered a method according to which the camera operator sensuously measures an approximate angle between the object surface and the sensing surface of the camera and such a measured value is input. However, it is extremely difficult for the camera operator to sensuously suppose a specific value of the angle of inclination in a state where there is no measurement reference. Further, even if the photographing position of the camera is at a short distance from the object, a relatively accurate angle of inclination cannot easily and rapidly be set.
Further, since the correction is performed based on the picked image data according to the above image distortion correcting method, a main object (e.g., white board) located obliquely from the camera needs to be photographed while being focused as a whole.
In the case that focal lengths of a plurality of objects within a field differ from each other, such as a case that a plurality of objects are to be photographed in an oblique direction, a method for deepening a depth of field by making an aperture of a diaphragm smaller is generally known as a photographing technique for attaining focusing conditions for all objects. In cameras provided with an automatic exposure control function (AE function), an exposure control value during photographing is automatically set according to the brightness of the object in accordance with a preset AE program. It is known that some of the cameras provided with the AE function are also provided, besides a standard AE program, with an aperture priority AE program for setting the exposure control value while prioritizing the aperture value. There have also been proposed cameras provided with multiple-spot metering function in which an aperture value is set such that a portion of an object within a field falls within a depth of field.
Even with the standard AE program, the aperture priority exposure control can be performed if a wide-angle lens is used since an exposure control is so performed as to make the aperture value as small as possible.
As a focus adjusting method in photographing an object which requires the above image distortion correction, a conventional method for making the depth of field as deep as possible may be adopted. However, with this method, influence of camera shake may occur and flash light may be required due to a low shutter speed, which limits a degree of freedom of the exposure control.
In the image distortion correction of the obliquely photographed image, it is sufficient to attain a focusing condition only for the entire main object within the field whose image is subjected to image distortion correction. It is not always necessary to attain a focusing condition for the entire field. Accordingly, if the depth of field is deepened more than necessary, the degree of freedom of the exposure control is considerably limited, making the photographing difficult.
In consideration of the above, the aperture value may be so adjusted as to attain the focusing condition for the entire main object which is subjected to the image distortion correction. However, with the existing cameras, even those provided with the aperture priority AE program, since the aperture value needs to be set by the camera operator, it is difficult to make such an aperture value adjustment.
On the other hand, the existing cameras capable of adjusting the depth of field to a portion of the object within the field do not enable the camera operator to accurately adjust the depth of field to an intended specific object within the field. Accordingly, it is difficult to perform a proper aperture control in conformity with the image distortion correction of the obliquely photographed image.
Further, in the electronic camera provided with the above image distortion correcting function, in consideration of the operability of photographing using the image distortion correcting function, it is desirable to confirm the correction result, preferably by monitoring an image after the correction before photographing.
It is an object of the present invention to provide an electronic camera which have overcome the problems residing in the prior art.
According to an aspect of the present invention, an electronic camera is provided with an image pickup device for photoelectrically picking up a light image of an object to generate image data, the image pickup device having a sensing surface residing on a first plane; an information provider for providing information on an oblique angle between the first plane and a second plane on which a surface of the object resides; a detector for detecting a distance to the object; and a corrector for correcting, based on the provided oblique angle information and the detected distance, the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane.
According to another aspect of the present invention, an electronic camera comprises: an image pickup device for photoelectrically picking up a light image of an object to generate image data, the image pickup device having a sensing surface residing on a first plane; an information provider for providing information on an oblique angle between the first plane and a second plane on which a surface of the object resides; and a corrector for correcting, based on the provided oblique angle information, the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane.
According to another aspect of the present invention, an electronic camera comprises: an image pickup device for photoelectrically picking up a light image of an object to generate image data, the image pickup device having a sensing surface residing on a first plane; a corrector for correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when a surface of the object is in parallel with the first plane when the surface of the object is on a second plane intersecting the first plane; and an aperture value setter for setting an aperture value in accordance with an angle between the first plane and the second plane.
According to another aspect of the present invention, an electronic camera comprises: an image pickup device for photoelectrically picking up a light image of an object to generate image data, the image pickup device having a sensing surface residing on a first plane; a corrector for correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when a surface of the object is in parallel with the first plane when the surface of the object is on a second plane intersecting the first plane; a size setter for setting a size of the light image on the sensing surface of the image pickup device; and an aperture value setter for setting, based on the set light image size, an aperture value to hold the surface of the object in a depth of field of the image pickup device.
According to another aspect of the present invention, an electronic camera comprises: an image pickup device for photoelectrically picking up a light image of an object to generate image data, the image pickup device having a sensing surface residing on a first plane; a corrector for correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when a surface of the object is in parallel with the first plane when the surface of the object is on a second plane intersecting the first plane; a calculator for calculating a correction permissible area of the light image; and a display unit for displaying the calculated correction permissible area.
According to another aspect of the present invention, an electronic camera comprises: an image pickup device for photoelectrically picking up a light image of an object to generate image data, the image pickup device having a sensing surface residing on a first plane; a corrector for correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when a surface of the object is in parallel with the first plane when the surface of the object is on a second plane intersecting the first plane; an image display unit for selectively displaying an actually picked up image in accordance with the generated image data and a pseudo image in accordance with the corrected image data; and a selector for providing a camera user with a selection of the actually picked up image display or the pseudo image display on the image display unit.
According to another aspect of the present invention, an image corrector comprises: an image data inputting portion for inputting image data which is generated by photoelectrically picking up a light image of an object with an image pickup device having a sensing surface; an oblique angle information providing portion for providing information on an oblique angle between the sensing surface of the image pickup device and a surface of the object; a distance information providing portion for providing information on a distance to the object; and a data correcting portion for correcting the inputted image data based on the provided oblique angle information and distance information so as to produce a pseudo object image identical to an image which is obtained when the surface of the object is in parallel with the sensing surface of the image pickup device.
According to another aspect of the present invention, a method for producing image data representing a pseudo object image whose surface resides on a plane parallel with an image picking up plane, the method comprises: picking up photoelectrically a light image of an object with an image pickup device having a sensing surface residing on a first plane; providing information on an oblique angle between the first plane and a second plane on which a surface of the object resides; detecting a distance to the object; and correcting, based on the provided oblique angle information and the detected distance, the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane.
According to another aspect of the present invention, a method for producing image data representing a pseudo object image whose surface resides on a plane parallel with an image picking up plane, the method comprises: picking up photoelectrically a light image of an object with an image pickup device having a sensing surface residing on a first plane; providing information on an oblique angle between the first plane and a second plane on which a surface of the object resides; and correcting, based on the provided oblique angle information, the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane.
According to another aspect of the present invention, a method for producing image data representing a pseudo object image whose surface resides on a plane parallel with an image picking up plane, the method comprises: setting an aperture value in accordance with an oblique angle between a first plane on which a sensing surface of an image pickup device resides and a second plane on which a surface of an object resides; picking up photoelectrically a light image of the object with the image pickup device at the set aperture value to generate image data; and correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane.
According to another aspect of the present invention, a method for producing image data representing a pseudo object image whose surface resides on a plane parallel with an image picking up plane, the method comprises: setting a size of a light image of an object on a sensing surface of an image pickup device, the sensing surface residing on a first plane, a surface of the object residing on a second plane intersecting the first plane; setting, based on the set light image size, an aperture value to hold the surface of the object in a depth of field of the image pickup device; picking up photoelectrically a light image of the object with the image pickup device at the set aperture value to generate image data; and correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane.
According to another aspect of the present invention, a method for producing image data representing a pseudo object image whose surface resides on a plane parallel with an image picking up plane, the method comprises: picking up photoelectrically a light image of an object with an image pickup device having a sensing surface residing on a first plane, a surface of the object residing on a second plane intersecting the first plane; calculating a correction permissible area of the light image; displaying the calculated correction permissible area; and correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane.
According to another aspect of the present invention, a method for producing image data representing a pseudo object image whose surface resides on a plane parallel with an image picking up plane, the method comprises: picking up photoelectrically a light image of an object with an image pickup device having a sensing surface residing on a first plane, a surface of the object residing on a second plane intersecting the first plane; correcting the generated image data so as to produce a pseudo object image identical to an image which is obtained when the first plane is in parallel with the second plane; and displaying selectively an actually picked up image in accordance with the generated image data and a pseudo object image in accordance with the corrected image data.